1. Field of the Invention
The present invention generally relates to glazing assemblies for vehicle tops and windows.
2. Description of the Known Technology
Plastic materials, such as polycarbonate (PC) and polymethylmethyacrylate (PMMA), are currently being used in the manufacturing of numerous automotive parts and components, such as B-pillars, headlamps, and sunroofs. Automotive vehicle tops and window modules represent an emerging application for these plastic materials because of various advantages in the areas of styling/design, weight savings, and safety. More specifically, plastic materials offer the automotive manufacturer the ability to reduce the complexity of the vehicle top and window assemblies through the integration of functional components into the molded plastic module, as well as to distinguish their vehicle from a competitor's vehicle by increasing overall design and shape complexity. The use of light weight plastic window and vehicle top modules may facilitate both a lower center of gravity for the vehicle (better vehicle handling and safety) and improved fuel economy. Finally, enhanced safety is further recognized through a greater propensity for occupant or passenger retention within a vehicle having plastic window and vehicle top modules when involved in a roll-over accident.
Although many advantages associated with implementing plastic vehicle tops and windows are recognized, these plastic modules will not see wide scale commercial utilization until existing regulations (e.g., Title 49, Chapter 5, Part 571.205 of the Federal Motor Vehicle Standard No. 205; ANS1-Z26.1 American National Standards Institute—1977) and various original equipment manufacturer (OEM) specifications, as established for glass windows, are met. In order to meet these requirements, protective layers (e.g., coatings or films) must be applied to the plastic window or vehicle top to overcome several limitations exhibited by plastic materials. These limitations include degradation caused by exposure to ultraviolet (UV) radiation, as exemplified by a color change, decreased optical transmission, and enhanced embrittlement (decrease in impact resistance), as well as both limited abrasion resistance and hydrolytic stability. Premature failure of the protective layer system, as indicated by delamination or adhesion loss, will result in a limited lifetime for the plastic window or vehicle top via the acceleration of the aforementioned degradation mechanisms. A darkening in the color or tint of the plastic window or vehicle top, for example, transparent clear (no tint)<solar (green tint)<privacy (dark tint), can facilitate premature failure of the protective layer system, presumably through an increase in the temperature at the interface between the plastic window or vehicle top and the protective layer system during environmental exposure. Since the weathering layer may be of different thickness (and therefore a variation in ultraviolet absorber (UVA) concentration) over the entire plastic window, premature failure is also observed where the weathering layer is thin (low UVA concentration). This same argument can be applied to the failure mechanism observed for other coated opaque plastic components (e.g., molding, B-pillars, tailgate modules, body panels, etc.) of various colors.
Therefore, there exists a need for a glazing assembly that will meet automotive regulatory and OEM requirements for windows and vehicle tops, as well as be robust against the occurrence of premature failure.